Many such catalytic systems have been identified in the past. For example, the following United States Patents disclose the use of many metallic catalysts, usually adsorbed onto catalytic supports, which can be used to catalyze cracking and related reactions. Such catalysts include various metals supported on titanates, e.g., zinc titanates. These patents include. U.S. Pat. Nos. 4,318,820; 4,313,017; 4,306,965; 4,263,133; 4,257,922; 4,244,809; 4,233,139; 4,151,123; 4,149,961; and 4,055,513.
Other United States Patents disclose various methods for impregnating titanium dioxide based supports with catalytic metals for use in a variety of reactions, including cracking reactions. In general, all of these prior art methods involve adsorption onto the conventional titanate substrate. For instance, U.S. Pat. No. 4,293,449 discloses the preparation of a catalyst by coating commercial supports with hydrated oxides such as Al.sub.2 O.sub.3.(H.sub.2 O).sub.2 and Na.sub.2 SiO.sub.3.(H.sub.2 O).sub.2 or hydrated titanate or zirconate salts (see Column 3, lines 39-44, of the reference) then calcining the coatings to form a high surface area material. This is followed by wetting of the support with solutions of salts of active metals and then drying of the catalyst. Reactive metals are impregnated into the catalyst by physical adsorption. U.S. Pat. No. 3,873,469 describes the preparation of a catalyst by wetting of a commercial support, including titania, zirconia, etc., with a metal alkoxide followed by hydrolysis and calcination to form an oxide coating. The active catalyst is prepared by wetting the surface of the support with a solution of active metal ions. Again, the metal ions are included in the catalyst by physical adsorption. U.S. Pat. No. 4,061,596 describes the preparation of a titanium oxide catalyst substrate. Among other methods, the latter is prepared by hydrolyzing titanium alkoxide to the corresponding hydroxide which is then calcined to form the oxide. Again, active metal ions are incorporated into the catalyst by physical adsorption methods. Other related processes are disclosed in U.S. Pat. Nos. 4,113,658 and 3,948,807.
A certain class of hydrous oxide ion exchange compounds have previously been investigated at Sandia National Laboratories for use in decontamination of aqueous nuclear waste (R. G. Dosch, "The Use of Titanates in Decontamination of Defense Waste", SAND-78-0710, Sandia National Laboratories, Albuquerque, NM, June 1978; R. G. Dosch, "Final Report on the Application of Titanates, Niobates, and Tantalates to Neutralized Defense Waste Decontamination--Materials Properties, Physical Forms, and Regeneration Techniques", SAND-80-1212, Sandia National Laboratories, Albuquerque, NM, January 1981) and as precursors for ceramic materials (D. L. Hankey et al, "Preliminary Investigations on Microstructure Development in PZT Ceramics", Abstract, 34th Pacific Coast Regional Meeting of American Ceramic Society, October 1981). Unlike the prior art catalytic supports, metal ions incorporated into these materials are contained therein not by physical adsorption but rather by ion exchange. Hence, although various properties of the known hydrous oxide ion exchangers might have suggested a potential for use as catalytic material, it could not be predicted or expected that such materials would in fact exhibit catalytic, hydrogenation or other related activity at least because of the presence of the metal ions via an ion exchange mechanism.